1. Field of the Invention
A distance measurement device measures the changing distance between the spring-supported bodywork and the vehicle axle in air-suspended vehicles with automatic levelling control unit.
2. Brief Description of the Background of the Invention Including Prior Art
The changing distance of the spring supported bodywork from the vehicle axle is based on a loading and an unloading of the vehicle. The measurement data of the distance measurement device are compared with an automatic levelling control unit to a set value referring to a reference level. In case of a deviation, the reference level is reinstated by a pressurizing or a venting of the air suspension. For a pressurizing of the air suspension, the automatic levelling control unit switches a solenoid control valve between the pressure means source and the air suspension to open a passage and causes the pressure means source to supply air into the air suspension until the automatic levelling control unit recognizes the reference level indicated by the distance measurement device. Thereupon, the air supply is discontinued and the solenoid control valve is closed. The venting occurs in such a way that the automatic levelling control unit switches the solenoid control valve to open passage into the atmosphere. The air suspension is then vented into the atmosphere for such time until the automatic levelling control unit blocks the connection to the atmosphere upon recognition of reaching of the reference level.
In addition to the reference level value, additional load-dependent values are automatically controllable such as, for example, damping and absorbing of driving vibrations. Depending on the suspended vehicle weight, for example, the damping and absorbing devices used for this purpose are influenced, such that the damping and absorbing properties and thus the driving comfort and the driving safety are retained for all possible weight situations.
In other automatic control devices, dependent also on the suspended vehicle weight, such as, for example, automatic load-sensing valves, an automatic control of the brake force of compressed-air brake cylinders at air-suspended vehicles with automatic levelling control unit is performed dependent on the air suspension bellows pressure. The load-sensing valve is controlled directly, like a relay, by the pressure of the air suspension bellows. However, additional mechanical means are required for the transformation of the air-suspension bellows pressure into a control signal usable by the load-sensing valve such as, for example, a control curve and a transfer element engaging the control curve.
The suspension bellows or the pressure line connected to the suspension bellows are to be furnished with additional measurement and signal transfer means for a transformation of the air-suspension bellows pressure into an electrical signal which is to correspond to the weight loading the air suspension. In addition to an increased expense of the device, this additional installation is associated with the disadvantage of increasing possible interference sources.
The German Printed Patent Document DE-OS 39 15 966 to Atsushi Mine et al. teaches a method and a device for the control of an active fluid-suspension system of a motor vehicle. While the reference teaches that the control unit 6 calculates the air amount to be entered into the suspension unit, there is no teaching in this reference for determining the weight of the load of the vehicle.
The German Printed Patent Document DE-OS 38 18 188 to Robert Schussler teaches an active suspension system. The reference teaches to calculate a correction of the support forces of the support aggregate 10 of the vehicle. However, the reference does not teach to determine the weight of the load of a vehicle.
The German Printed Patent Document DE-OS 38 15 612 to Matthias Fahrnschon et al. teaches a method for the control of a compressed air supported vehicle suspension. The reference teaches a system which takes care that the pressure difference between the air suspension elements 1 and 2 is lower. No teaching is seen in this reference relating to weight determination of the load of the vehicle.
The German Printed Patent Document DE-OS 35 25 835 to Roland Blanz teaches a device subjectable to the motions between the vehicle chassis and the vehicle axles at motor vehicles. The reference teaches to employ a path sensor 23 for furnishing an electrical signal corresponding to the path of a linkage. The reference does not contribute to the measurement of a weight of a load of a vehicle.
The German Printed Patent Document DE-OS 2,306,154 to Regie Nationale des Usines Renault teaches a combined device for correcting of the braking and of the vehicle position in road vehicles. While the reference teaches obtaining of a correction of the position of a motor vehicle relative to the road, no suggestion is made as to determining the weight of a load of a vehicle.
The U.S. Pat. No. 4,832,141 to Richard L. Perini et al. teaches vehicle mounted load indicator system. The system employs air bags and pressure changes in air bags and a first conduit serving the air bags are communicated to a transducer or the like by a second circuit. A readout device is located in the vehicle operator station. The readout device displays the weight of the load on the platform and is adapted for use with different-sized air bag components. While the reference teaching refers to the determining of pressure changes in air bags, there is no teaching in this reference as to an automatic control of the level of the chassis box versus the axles.